Fottea

Fottea 9(2): 299-306, 2009 | DOI: 10.5507/fot.2009.029

Ultrastructure of a Hyalodiscus species (Bacillariophyceae; Subclass: Coscinodiscophycidae, Fam. Hyalodiscaceae) from brackish waters of Tonga, Oceania.

Eugen Rott¹, Werner Kofler¹, Robert Schabetsberger²

¹ Institute of Botany, LF University of Innsbruck, Sternwartestrasse 15, A-6020 Innsbruck, Austria

² Division of Organismal Biology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria

A rarely recorded centric diatom of the genus Hyalodiscus was found in three mixed freshwater and brackish environments of Tonga. Both classical morphological and scanning electron microscopic features were used to classify the taxon within currently know taxa from inland and brackwater sites. We recorded stable ultrastructural features (e.g. type of poroids, type and arrangement of rimoportulae) but also several variable morphological features (mainly outline, diameter and structure of the umbilicus and nodulation within the umbilicus centre) as well as variable ultrastructural features (margin of central area; central termination of striae). The loculate nature of puncta closed by rotae and the small fultoportulae potentially typical features for the genus was confirmed. The taxon showed a high similarity to Hyalodiscus lentiginosus JOHN 1982 described from Swan river estuary Australia with the exception of more variable punctation in the central umbilicus area and different variability of central noduli. We also checked for identical features (size, central area) with Hyalodiscus withneyi described by EHRENBERG 1870 from near Great Salt Lake Utah.

Keywords: centric diatom, epibenthic habitat, loculate poroids with rotae, primitive rimoportulae, umbilicus variability

Received: April 30, 2009; Accepted: June 26, 2009; Published: September 1, 2009  Show citation